Contact lenses made from silicone-containing materials have been investigated for a number of years. Such materials can generally be subdivided into two major classes: hydrogels and non-hydrogels. Non-hydrogels do not absorb appreciable amounts of water, whereas hydrogels can absorb and retain water in an equilibrium state. Hydrogels generally have a water content greater than about five weight percent and more commonly between about 10 to about 80 weight percent. Regardless of their water content, both non-hydrogel and hydrogel silicone contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
Surface structure and composition determine many of the physical properties and ultimate uses of solid materials. Characteristics such as wetting, friction, and adhesion or lubricity are largely influenced by surface characteristics. The alteration of surface characteristics is of special significance in biotechnical applications, where biocompatibility is of particular concern. Therefore, those skilled in the art have long recognized the need for rendering the surface of contact lenses and other medical devices hydrophilic or more hydrophilic. Increasing the hydrophilicity of the contact-lens surface improves the wettability of the contact lenses with tear fluid in the eye. This in turn improves the wear comfort of the contact lenses. In the case of continuous-wear lenses, the surface is especially important. The surface of a continuous-wear lens must be designed not only for comfort, but to avoid adverse reactions such as comeal edema, inflammation, or lymphocyte infiltration. Improved methods have accordingly been sought for modifying the surfaces of contact lenses, particularly high-Dk (highly oxygen permeable) lenses designed for continuous (overnight) wear.
Various patents disclose the attachment of hydrophilic or otherwise biocompatible polymeric chains to the surface of a contact lens in order to render the lens more biocompatible. For example, U.S. Pat. No. 5,652,014 teaches amination of a substrate followed by reaction with other polymers, such as a PEO star molecule or a sulfated polysaccharide. One problem with such an approach is that the polymer chain density is limited due to the difficult of attaching the polymer to the silicone substrate.
U.S. Pat. No. 5,344,701 discloses the attachment of oxazolinone or azlactone monomers to a substrate by means of plasma. The invention has utility in the field of surface-mediated or catalyzed reactions for synthesis or site-specific separations, including affinity separation of biomolecules, diagnostic supports and enzyme membrane reactors. The oxazolinone group is attached to a porous substrate apparently by reaction of the ethylenic unsaturation in the oxazolinone monomer with radicals formed by plasma on the substrate surface. Alternatively, the substrate can be coated with monomers and reacted with plasma to form a cross-linked coating. The oxazolinone groups that have been attached to the surface can then be used to attach a biologically active material, for example, proteins, since the oxazolinone is attacked by amines, thiols, and alcohols. U.S. Pat. No. 5,364,918 to Valint et al. and U.S. Pat. No. 5,352,714 to Lai et al. disclose the use of oxazolinone monomers as internal wetting agents for contact lenses, which agents may migrate to the surface of the contact lens.
U.S. Pat. No. 5,804,318 to Pinchuk et al. discloses lubrifying coatings for reducing the coefficients of friction of surfaces on medical devices, including hydrophilic copolymers containing some monomers having pendant tertiary amine functionality. The hydrogel coatings are covalently bondable to epoxy functionalized surfaces on the medical equipment.
U.S. Pat. No. 4,734,475 to Goldenberg et al. discloses the use of a contact lens fabricated from a polymer comprising oxirane (epoxy) substituted monomeric units in the backbone, such that the outer surfaces of the lens contain a hydrophilic inducing amount of the reaction product of the oxirane monomeric units with a water soluble reactive organic, amine, alcohol, thiol, urea, thiourea, sulfite, bisulfite or thiosulfate.
In view of the above, it would be desirable to find an optically clear, hydrophilic coating for the surface of a silicone medical device that renders the device more bicompatible. It would also be desirable to form a coating for a silicone hydrogel contact lens that is more comfortable for a longer period of time, simultaneously tear-wettable and highly permeable to oxygen. It would be desirable if such a biocompatibilized lens was capable of continuous wear overnight, preferably for a week or more without adverse effects to the cornea. Further, it would be desirable to provide a coating with these properties that can be readily renewed to restore its properties to an as-new state.